So this has happened to my girlfriend a couple of times and she was tired of losing her data and cookies. So I have a method that seems to work without deleting the data. I don't know if this means it will come back more frequently, but so far, so good. (So far being a solid 2 hours of online browsing for reclaimed nick-knacks from the far flung corners of our wonderful world.)
1. double click home button and close all running applications (maybe just need to close safari, don't know)
2. click on safari app (is click the right terminology?)
3. (the tricky part) click on the x on the address bar before the malicious tab opens again (you have to be fast, have one finger ready to press the x as you open safari with the other hand/finger {i don't know how big your hands are}).
4. repeat steps 1-3 until you get it to work, took me about ten tries
5. open a new web page in naughty tab
6. open a new tab
7. close Mr.-bad-guy-we-just-thwarted's tab
This might work by clicking on other open tabs, the back button, etc.., but the x in the address bar definitely works. Basically you have to interupt the malicious website before it can load, but it happens really quickly.
Good luck!
P.S. Should I post the website I think is causing the problem (most likely not intentionally)? I am no expert, so i have no certainty and don't want to cause problems for what may be a genuine business that got hacked or hijacked or whatever happens to good guys when the internet get a hold of them, but maybe someone can look into it.